Intake, digestion, and nitrogen utilization by sheep fed tropical legumes with contrasting tannin concentration and astringency.

Abstract

We conducted an experiment to determine the effects of concentration and astringency of extractable and bound condensed tannins (CT) in tropical legumes on intake, digestibility, and nitrogen (N) utilization by sheep. The test legumes (Desmodium ovalifolium and Flemingia macrophylla) had similar concentrations of extractable CT (90 g/kg DM) but different concentrations of bound CT and astringency of tannins. Chopped, sun-dried forage of each legume was sprayed with either water (control) or polyethylene glycol (PEG, 35 g/kg of DM) to bind extractable CT and fed daily (26 g/kg BW) to eight sheep with ruminal and duodenal cannulas. The sheep also received starch-extracted cassava meal intraruminally (4 g/kg BW) as a constant source of readily fermentable carbohydrates. Intake of the two legumes was not different (P > .05), but it increased an average of 10% (P < .01) when extractable CT were reduced from 90 to 50 g/kg of DM with PEG. Ruminal and total tract digestibilities of OM, NDF, and ADF were greater (P < .01) with D. ovalifolium than with F. macrophylla and increased for both legumes with the addition of PEG. Greater (P < .01) N flow to the duodenum, N absorbed from the intestine, and fecal N were observed with F. macrophylla than with D. ovalifolium. Extraction of CT with PEG resulted in less (P < .05) ruminal escape protein and less (P < .01) fecal N with both legumes, but apparent postruminal N digestion was not affected. Changes in the concentration of extractable CT in tropical legumes can significantly affect forage intake, digestion, and N utilization by sheep.

A review of the effects of forage condensed tannins on ruminal fermentation and bloat in grazing cattle

“…The pattern of reduced nitrogen digestibility in the rumen accompanied by increased NAN flux to the small intestine is typical for forages containing CT Wang et al 1996a;Barahona et al 1997). Although total apparent digestibility of N is usually reduced in animals fed diets containing CT, due to higher faecal nitrogen excretion , these values can be misleading because they do not take into account the benefits of shifting the site of N digestion from the rumen to the intestine.…”

Value Addition of Feed and Fodder by Alleviating the Antinutritional Effects of Tannins

“…These were leaves-Acacia brevispica, A. nilotica, A. tortillis, Salix caprea and S. viminalis fed to sheep, goats and cattle [38,44,45,114,121,131,134,140], C. calothyrsus, Onobrychis viciifolia fed to goats, lambs and cattle [68,108,151,221] carob (Ceratonia siliqua), Lespedeza cuneata, Prosopis cineraria, Quercus semecarpifolia given to goats [30,188], Desmodium ovalifolium, Dorycnium rectum, Hedysarum coronarium, Lotus corniculatus, L. pedunculatus fed to sheep [13,122,150,201,210] and Leucaena leucocephala given to ruminants [72,118]. The fruits-Acacia tortillis, Dichrostachys cinerea given to goats [105,128], honey locust (Gleditsia triacanthos) avidly eaten by sheep [31] and acorns of Quercus rotundifolia, found to be excellent for Mediterranean pigs and ruminants [34], were also used for animal feeding.…”

“…It has, however, both beneficial and adverse effects in ruminants. The incorporation of PEG in the diet has beneficial effects, particularly for tanniniferous feeds having of 5-10 % content of CTs [12,19,20,86,164,188,190,191,201,225]. The PEG-inactivation of tannins increases voluntary feed intake, availability of nutrients and decreases microbial inhibition in degrading the tanniniferous feeds, which in turn increases the performance of animal.…”

Determination of some digestibility of nutrients, rumen and blood metabolites of Akkaraman rams fed low-tannin sorghum and other conventional feeds

“…Barry and Duncan (6) stated that decreasing tannin content by PEG addition to Lotus pedunculatus increased digestibility from 0.547 to 0.627. In other study (5), PEG addition to Desmodium ovalifolium decreased CT content from 90 to 50 g/kg and increased OM digestion from 36.1 to 43.5% while total digestibility increased slightly. Possibly, due to low-tannin content, our results were in agreement with literature in terms of OM digestibility.…”

“…Moreover, tannins directly affect digestibility of plant cell walls by binding to microbial enzymes in the rumen. Tannins may further reduce digestibility of cell wall carbohydrates by forming indigestible complexes with cellulose and hemicellulose (3,5,7,17,18).…”